Charging System Issue

[682bear]

I have a 1940 Ford Deluxe Fordor with a 59A flathead... it is still 6v positive ground and still has the 6v generator.

When I first bought the car, I was checking to be sure the charging system was working... the dash guage showed it wasn't. I have an analog voltmeter and a digital multi-meter. The analog showed a steady 7.5v across the battery with the engine running. The digital was fluctuating wildly between 3.5v and 5.5v at idle, dropping to 1.5v to 3.5v revved up some.

I drove it to town one day last week... when I tried to crank it to come home, the battery was too weak to crank it. After having it hauled home, I charged the battery... it took a charge just fine and would crank the engine.

I took the generator to a generator/alternator rebuild shop... they tested it and declared it to be good. I've installed a new voltage regulator, new negative battery cable, and new 6v NAPA battery...

I also removed all of the cables and wires associated with the charging and starting systems and made sure the connections were all clean and tight... including the ground straps from the body, block, and frame.

Nothing has changed... the digital tester still fluctuates from 3.5v to 5.5v at idle and 1.5v to 3.5v revved. The dash guage needle stays in the yellow field... it never gets into the green.

I checked my digital meter against one of the cheap 'giveaway' Harbor Freight meters... it reads very close to the same...

I can't think of anything else that could cause the issue... unless I've lucked up and had either two faulty regulators or two faulty digital meters...

Any other ideas?

Thanks- Bear

[Bob C]

Digital meters and the old Ford ignition system don't play well together, use
the analog meter.

[682bear]

Originally Posted by Bob C

Digital meters and the old Ford ignition system don't play well together, use
the analog meter.

I was wondering about that... about whether I was getting 'interference' with the digital meter... what would cause that?

-Bear

[FortyNiner]

Try adding another ground directly to the generator. Worked on my '46 with a similar issue.

[Terry,OH]

The digital meter will see the high voltage spikes from the ignition system and give false readings.

Suggest you turn on the vehicle bright lights for about 2 minutes turn lights off, Read battery voltage should be between 6.25 to 6.6 volts or higher Then start the car. With the headlights off, meter across the battery, increase engine RPM well above idle, read the charging voltage after it settles down. Should be between 7.2 to 7.5 V.

The battery should be able to hold a charge with the bright lights on, and the voltage regulator can be adjusted to give the proper charging voltage.

[Kube]

Sponsored Links (Register now to hide all advertisements)

Many folks paint the generator as well as the intake in full. There should be no paint between the adjacent mounting surfaces of those parts.
Be certain your pieces are free of paint in those areas.

[ford38v8]

Mike, you may well have nailed it. Funny thing about these electrical systems… They can run and run and run till the battery is dead with poor connectivity, but cannot accept a charge from the generator with those same poor connections.

[682bear]

There is some good info and ideas here... thanks!

I didn't consider the generator ground... that's definately something I'll have to check. I do understand that any amount of resistance in the circuits has a bigger effect on a 6v system than it would on a 12v system.

Thanks again!

-Bear

[Bill OH]

I ran a 16ga wire between the generator housing and the regulator frame and a digital ohm meter connected across those two points should read zero ohms with clean connections. Generator and regulator now respond very well - no fluttering of the ammeter.

Next, I found that ground for the starting circuit went from the battery plus to the firewall and about 18 inches further away, the ground strap for the motor was connected to the firewall and then to the motor - result 0.35 volt drop. I ran a 1 gauge copper cable with copper eye soldered with silver bearing solder from the battery plus to the firewall where the engine ground strap was connected with connections sanded clean and tight. Voltage drop now 0.1 volts. Steel does not have the conductivity that copper does - many rungs down the ladder. The starter is much more responsive.

[682bear]

Ok, I'm back working on the '40...

I still haven't figured out the charging system... I'm using an analog voltmeter... across the battery while not running, I'm getting 6.3 volts. At idle, 6.4v... it stays at 6.4v as I rev the motor.

I cleaned the points in the original regulator and reinstalled it... no change, still 6.4v running.

Connecting the voltmeter between the armature connection and ground, I get 1.5v at idle, up to 2.5v as it revs up.

I found an old post here that said to disconnect the field wire from the regulator and, at 1500 rpms, momentarily touch it to the armature connection to see if the voltage rises. I did that... very briefly... the voltage went over 8v...

I've checked the resistance from the generator housing to the regulator housing... it shows 0 ohms... I did add a ground wire from the generator to a mounting screw on the regulator before I started all of this, but it didn't change anything.

I don't know where to go from here...

-Bear

[big job]

If I read this correctly, you jumped the field wire and got 8 volts; that rules out the generator have you jumped the field wire to the Bat terminal? Looks like there is no
field signal from the regulator. Also is the cutout closed or open when running. If open
close it with your finger. Regulator could be way out of adjustment also check the resistors on the back of the regulator...

[682bear]

The 'cutout'? Would that be the set of points at the coil above the 'BAT' terminal in the regulator? They seem to stay open, where the other two sets seem to remain closed.

With the voltmeter connected to the 'ARM' terminal and a ground, it shows about 1v... if I push that set of points closed, the voltage goes up to 6.4v.

I did polarize the regulator after I installed it.

-Bear

[cas3]

No cutout on a 40 ford, you have a 2 brush gennie with a regulator.

[682bear]

That's what I was thinking... but I don't know a lot of the technical jargon...

-Bear

[FlatheadTed]

It is a regulator but part of that is a cut out and as you say its above the Bat connect . ,jhat should close when charging , you can use a amp meter but between battery and earth strap , add a jumper to the earth then start it then remove it leaving the Amp meter .Ted

[Alaska Jim]

Voltage above idle ( about 1500 rpm ) should be a bit over 7 volts. you may have to adjust the voltage regulator